Apparatus fob cutting threads



June 9, 1953 c. B. KEYS 2,641,287

APPARATUS FOR CUTTING THREADS Filed NOV- 21, 1949 QAQENCE BRANT firs,

mmvron Patented June 9, 1953 UNITED STATES PATENT OFFICE APPARATUS FOR CUTTING THREADS Clarence Brant Keys, Sherman Oaks, Calif. Application November 21, 1949, Serial N 0. 128,543

2 Claims.

This invention relates generally to an improved apparatus to be used in conjunction with a conventional lathe for cutting screw threads and more specifically relates to such an apparatus adapted to cut threads in non-metallic cylindrical objects.

Cutting threads in non-metallic objects, and particularly in wooden objects, has presented problems not heretofore satisfactorily solved. Prior cutters have not been adapted to rapidly make smooth cuts, with the result that rough surfaces and burrs remain on the threads after the cutting operation and devices for rapidly cutting threads have not been available. Snug fitting of male and female members threaded together is thus made impossible without a sanding or polishing operation following cutting.

My novel cutting tool is adapted to be used in conjunction with a conventional lathe equipped with a carriage selectively engageable with a lead screw so that the carriage may be moved longi tudinally of the lathe in timed relation to the rotation of the lathe chuck. The tool of my invention is rotated by an auxiliary motor at very high speed, and th cutting blades exert a shaving effect to remove only a very thin slice of material with each stroke. The blades are designed to cut, sequentially, one side of a thread and then the other, and the blades are raked back to provide a small angle of clearance so that the portion of each blade immediately trailing th cutting edge performs a polishing operation on a minute section of the work piece or object on which a thread is being cut.

The cutting tool of my invention may be made to form internal threads with as great facility as external threads, and the depth of threads cut on either male or female objects may be selectively adjusted by the operator to any value within the range of the tool,

The principal purpose of my invention is therefore to disclose an apparatus including a novel cutter for cutting screw threads.

Another object is to disclose such an apparatus wherein the cutter is rotated at a speed very much greater than the speed of rotation of the Work piece.

A further object is to disclose a thread-cutting apparatus including a cutter which is adapted to sequentially cut one side and then the other of a screw-thread in rapid succession.

A further object is to provide an apparatus, ncluding a cutter, having the above characteristics and adapted to form a thread of any desired depth within the range for which the cutter is designed.

Another object is to disclose a thread-cutting tool adapted to form internal threads as well as external threads on non-metallic objects.

Other objects and advantages will become apparent from the following description of an exemplary form of the invention taken in connection with the accompanying drawing, in which:

Fig. 1 is a side elevational view. of a lathe with the apparatus of my invention in position for cutting a thread.

Fig. 2 is a fragmentary plan view, partly in section, showing the cutting operation of one blade of the cutter. Y

Fig. 3. is a view similar to Fig. 2 but showing the cutting operation of the other blade of the cutter.

Fig. 4 is a fragmentary perspective view of the two blades and part of the shank of the cutter.

Fig. 5 is an end view of the cutter.

Fig. 6 is a fragmentary view taken on line VI-VI of Fig. 5.

Generally speaking, my invention contemplates the use of a lathe equipped with a conventional carriage longitudinally movable on the bed of the lathe, the carriage having mounted thereon a high-speed motor driving a cutter in en gagement with the work piece carried by the chuck of the lathe.

Referring in detail to the drawing, a lathe indicated in its entirety by H) has a conventional chuck l l adapted to hold a work piece I2. Motor I5 is mounted on cross-slide l6 and is adapted to be moved transverse to the axis of lathe ill in a horizontal plane by hand crank ll. The entire carriage assembly [8 may be moved parallel to the axis of chuck ll either manually by hand wheel I9. or automatically by connection to lead screw 20. Motor I5 is mounted so that its output shaft 22 is parallel to the axis of chuck I l.

Secured to shaft 22 of motor I5 is tool-holding chuck 23, which firmly engages shank 25 of cutter 24. Movement of carriage l8 transverse or longitudinal of lathe l0 thus correspondingly moves cutter 24, and the longitudinal axis of the cutter is maintained parallel to the axis of chuck l I at all times.

As best seen in Fig. 4, cutter 24 is provided at one end with two blades 26 and 2]. Each blade has a cutting edge indicated at 28 and 29 respectively and outermost points 3| and 32. The line joining outermost points 3| and 32 is perpendicular to the axis of shank 25 of cutter 24.

With particular reference to Fig. 2, cutter 24 is shown with blade 2'! cutting one side of a thread in work piece 12. Similarly, in Fig. 3 the other blade 26 of cutter 24 is shown cutting the opposite 28 and 29 of blades 26 and 21 are curved in outline. Each cutting edge lies in a plane and the planes of the two cutting edges are parallel to each other. These parallel planes are inclined to a plane normal to the axis of shank 25 in two. coordinates. First, as clearly shown in Figs. 2 and 3, the apparent inclination of the cutting edge planes to the said normal plane as projected on the coordinate plane represented by the plane of the drawing is at an angle equal to one-half the root angle of the thread being out. Secondly with particular reference to Fig. 6, the angular incl na n of t e cut ing dg lan s wi h espe t t t e ai normal plane as proj t d on h co: ordinate. plane r pre ent d y t plan oi the r ng. n g- 6 i a sm l cle ance. an le, i e t at 3 I have found that a c arance ng e as t us defined, Q f m to ives i ab r su .-v In gener th c arance angle sh u be smal er f r e arder Woo st wa 1 0 1 u ab e th a l n .l0 l 'l outermost points SI and 32 of blades 2.6 and 2] is perpendicular to the axis of shank 25. It can therefore be seen that said outermost points will cooperatively cut the root of a screw thread, and because of the high speed of rotation of cutter 24 relative to the speed of, rotation of work piece I2, points SI and 32 will make successive cuts at almost the same point in work piece I2. In cutting threads, carriag I8 is moved alongthe bed of lathe I0 in timed relation with the rotation of chuck I I by the action of lead screw 28 in familiar manner. Thus motor I5 and cutter 24 are carried toward chuck II and work piece I2 by the leftward movement of carriage l8, and cutter 214 will cut a smooth helical thread On work piece I2.

I have found that when work piece I2 is between 1" and 2" in diameter, composed of wood, plastic or similar material, and is rotated at about 60 revolutions per minute, my cutter should be driven at a speed between about 10,000 and 30,000 revolutions per minute. In general, the more rapidly the cutter is rotated relative to the workpiece, the smoother will be the finished thread. It can be readily understood that each cut made by the shaving action of the rapidly rotating cutter :24 removes a very thin layer of material from work piece I2. .After each cut the outer surface of each blade immediately trailing the cutting edge thereof performs a polishing function on the side. f the thread just out.

Thus I have provided a cutting tool capable of producing a smooth thread, cove, shoulder .or o ve in obje ts of; weed and other material 01; similar characteristics and adapted to out male or female threads with eq aliae ity wi h a shaving action. ltwlll be apparent to thqsezskilled in.

4 the art that certain changes and modifications" can be made Without departing from the spirit of the present invention. All such modifications are intended to be embraced within the scope of the appended claims.

1. A milling tool for cutting threads in a rotatable work piece comprising: a rotatable shank provided with a pair of symmetrically disposed, radially extending blades, each blade having an outer surface lying in a plane deviating from a plane perpendicular to the axis of the shank by one-half the root angle of thread to be cut, said Sl riaces facing in opposite directions, each of said planes terminating in a curved cutting edge, the points along such edge on each of the blades farthest removed from the axis of the shank lying in a common plane perpendicular to the shanlg axis and constituting cutting points for the root of a thread; the outer surface of each blade being raked. back rom sa d cuttin edges whe eby sa d planes are inclin d t th shank in We team ates; .eorr nenfle po nt along, aid cu ved cu t n ed s, at p g e sively s or er distances item the shan a is, be ng at progressively greater distances from the common plane perpendicular to the shank axis and in w ich a d out rmost poi ts e 2 In eh pp at s fer cutti g r s nnermetal ic obj ts o ylind i a fo m the cem ine tion of means for rotating a cylindrical object about tsv axis; a cutter shank unt d r tation about an axis llarallel to but spaced from the a is of th object; and mea s r nc g: t e sh -11k al n its axis of rotation in timed reletl n t t e rotat n off he ob t; aid h nk bein p ided with a pair o mm t al dis.- e-ee l r di y exten i cutt ng l d s eac b a e ha ing an outer surtae yin n e lane v t ng f om p ane pe p nd cular to h axis f the s am; by hali the ot a le f h e d o e ut said suriae s f c n n. pp i e iree tio s ch of said planes. te m na ing in. a cur ed ut ed e th points a o g such ed e o each of. the bladesv farthest. removed from the axis of t e shank. y ng in a common plane. n inem iellle t0 he shank axis ande stitutingcutt ns po ts fo he root of a thread; h u er sur ace of h b e b ng a ed back from said cutting es here y aid planes are incl ned the shank axis n wo teammates; correspondin Pei s alon said curred cutt n ed es, a ro gressi ly sho ter distanc s. rom thefsha kaxis, being at progressively greater distances from the. c mmon lan pe pendicular to the shank ax and w ich .se doute lnee po nts he CL RE E B ANT Name Date, ,Calahan Sept. 19, 1911 Thomas May :31. 1338,

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